Disposable oxygen exchanging devices, known as oxygenators, have been long known and used in the medical field, with the purpose of releasing oxygen to blood and removing excess carbon dioxide from patient blood during extracorporal circulation treatments.
These prior art devices consist of substantially cylindrical bodies, which enclose an oxygenation chamber with a gas exchanging unit arranged therein.
The latter typically consists of a multitude of hollow fibers, which are arranged substantially parallel to each other and to the longitudinal axis of the cylindrical body, have a lumen as large as a few hundreds of microns, and are formed of a flexible membrane, which is only gas-and not fluid-permeable.
The ends of the hollow fibers are incorporated in two corresponding solid connection elements, known as “pottings”, which are typically formed of polyurethane-based glues.
In practice, the container bodies of these oxygenator devices, hereinafter simply referred to as oxygenators, have a first blood inlet and outlet pair, with blood being forced to flow in a predetermined path within the oxygenation chamber, and to lap the hollow fibers in a flow direction substantially perpendicular thereto, thereby becoming richer in oxygen and releasing excess carbon dioxide.
The cylindrical body also has a second inlet and outlet pair, designed both for supplying oxygen gas, in pure form or diluted with other gases, such as nitrogen, and for discharging the carbon dioxide released to blood during oxygenation.
These oxygenator devices are typically combined with heat exchangers, which are required for temperature control of the blood flowing in the extracorporeal circuit of the patient to be treated, and which typically use water “treated” by a heating device or cooling water to add or remove heat from patient's blood, and are generally known as “heaters” or “coolers” or otherwise generally defined as “temperature baths”.
Typically, for operation of these oxygenators, after such passage through a temperature control apparatus to reach a desired temperature, the blood to be oxygenated that comes from the patient and is carried by a transport conduit shall enter the oxygenation chamber through the inlet therefore, lap the multitude of hollow fibers having oxygen, or a mixture of oxygen and other diluting gases, flowing therein, receive oxygen and simultaneously release carbon dioxide as a result of differential concentrations, and eventually flow out of the outlet in an oxygen-enriched state, to finally reach the patient through a return connection line.
Oxygen, or the oxygen-containing gas mixture, enters its inlet and is released to blood while carbon dioxide is released by blood to the depleted oxygen that flows in the hollow fibers and us discharged through the outlet.
The motion of blood flow that comes from the patient, passes through the oxygenator and goes back to the patient is typically generated and maintained using a pump that may be mounted along an extracorporeal circuit that establishes connection between the patient and the oxygenator.
The pump action generates a pressure higher than atmospheric pressure in the oxygenator, which is sufficient to overcome the sum of the mechanical resistances encountered by blood as it flows through the treatment chamber that contains the hollow fibers, through the conduits that connect the various devices and those of the peripheral circulatory system of the patient, to ensure that circulation is maintained active all along the path defined by the extracorporeal circuit.
An additional requirement to be met by these oxygenators is to provide an exchange surface area that is optimized relative to their overall size, which has to be maintained within strict limits both due to bulk limitation and handling requirements, and because a volume of blood has to be removed from the patient to fill the device and the circuit attached thereto, even though it is diluted with suitable salines.
An oxygenator as described above is known from U.S. Pat. No. 5,817,278.
This patent discloses an oxygenator having a cylindrical body which is composed of an outer wall and an inner wall, arranged in concentric relation to the outer wall and having a smaller diameter, so that a gap, forming the oxygenation chamber, is defined between these inner and outer walls.
This chamber, which has inlet and outlet paths in communication with the outside, holds a set of hollow fibers arranged therein, which are made, as mentioned above, from a membrane that is only permeable to gases, and in which oxygen is caused to flow.
This set of hollow fibers comprises fibers in such number as to circumscribe the inner wall and wrap it until it laps the outer wall, and is kept at a distance therefrom at certain predetermined points by means of a series of longitudinal ribs that project out of the facing surfaces of the inner and outer walls and act as spacers.
Thus, a plurality of free longitudinal passages remain between the set of hollow fibers and the inner and outer walls, which passages are filled with the blood flow as it passes through the oxygenator and generate a substantially wavy flow that passes through the winding of hollow fibers thereby capturing the oxygen flowing therein and releasing the carbon dioxide carried to the outside.
Another oxygenator device is known from patent EP 1 557 185.
This patent discloses an oxygenator having, like the one described above, a hollow cylindrical body that defines an internal oxygenation (or exchange) chamber within which a winding of hollow fibers is arranged.
Once again, the ends of the hollow fibers are embedded in two corresponding end elements known as “pottings”, and formed of plastic material.
The oxygenation chamber is composed of two half-chambers, each holding a corresponding winding of hollow fibers, so that the latter are perpendicular to an inlet and an outlet for the blood to be oxygenated, and in opposed relation.
Each of the windings of hollow fibers defines a smaller chamber at its center, containing a diaphragm, that consists of a solid and substantially flat body, hence impermeable to blood flow, whose ends are held in contact with the winding of hollow fibers.
This diaphragm has a cross section with surfaces that push back the blood flow as it impinges against it in the path between the inlet and the outlet and deflect it towards the winding of hollow fibers, thereby imparting a wavy motion in the blood flow to be oxygenated, which is caused to pass through the winding of hollow fibers at multiple areas, thereby creating the desired exchange between oxygen and blood and between the carbon dioxide released from the blood and the hollow fibers that form the winding.
Two adjacent, isolated chambers are defined in the body of the oxygenator according to this document, which chambers are arranged in mirror-like arrangement with respect to a median plane of symmetry.
The first chamber uses a winding of non porous plastic capillaries for thermostating the blood that laps the exterior surfaces thereof, with the thermostating fluid, typically water, flowing in the capillaries; on the other hand, the second chamber uses a winding of hollow fibers arranged therein which are formed of a microporous membrane, and are used to transfer oxygen to the blood that laps the exterior surfaces of these hollow fibers, while oxygen flows therein.
Furthermore, a series of longitudinal parallel passages are provided, also in mirror-like arrangement, which facilitate the passage of blood flows and have the purpose of breaking the laminar flow and improve the effectiveness of the oxygenation and carbon dioxide removal process.
This prior art suffers from certain drawbacks.
A first drawback is that the increase of pressure losses caused in prior art oxygenators by resistance to blood flow motion damages the red cells membranes and causes hemolysis, i.e. red cell (or erythrocyte) destruction.
A second drawback is that prior art oxygenators require their oxygenation (and exchange) chambers to be filled with considerable volumes of blood, to be withdrawn and removed from the patient to fill the conduits of an extracorporeal circuit, which volumes are possibly compensated for with additional adequate volumes of blood compatible diluents.
A third drawback is that prior art oxygenators tend to be exposed to quick deterioration of gas exchange performance.
A fourth drawback is that if prior art oxygenators are not used within a short time from their fabrication and are not stored using criteria that can ensure stable effectiveness thereof, they tend with time to be exposed to degradation of the components mainly made of plastic materials.
This degradation may generate deformations of components and thus create undesired gaps or apertures that will act as free passages for blood that will flow through them without previously lapping the hollow fibers and without being adequately oxygenated and washed out of excess carbon dioxide, before reaching back the patient.